1. Field of the Invention
The present invention relates to a control device for an automatic transmission and more particularly to a control device for an automobile transmission suitable for a vehicle such as an automobile.
2. Description of the Prior Art
Conventionally, this kind of control device for an automatic transmission is provided with a shift-locking device which locks a shift lever for safety when the shift lever is positioned in a parking position and a brake pedal is not depressed.
The shift lever comprises a control lever pivotably mounted on a base bracket, and a compression rod contained by the control lever in a slidable manner in the axial direction and mounted with a positioning pin in the direction perpendicular to the above axis. The control lever is provided with a guide slot at the peripheral portion for guiding the movement of the positioning pin.
The shift-lock device comprises a lock bushing fitted on the control lever in a freely pivotable and axially immovable manner, and a lock solenoid for pivoting the lock bushing to a lock release position, mounted on the control lever through a mounting bracket.
According to this configuration, when the shift lever is positioned in the parking position, the descent of the positioning pin is blocked by the lock bushing, so that the shift lever is shift-locked. In this shift-locking condition, when the break pedal is pressed, the lock solenoid acts to pivot the rotary bushing to the shift-lock releasing position to release the shift-lock.
In addition, when releasing the shift-lock, if an electric system does not work, a lock releasing lever can be operated manually to pivot the lock bushing to a shift-lock releasing position through some intermediates.
However, in a conventional control device for an automatic transmission, the guide slot of the control lever is usually formed by a punch press operation. As a result of the punching operation, the control lever is deformed into elliptical cross-section near the slot. The lock bushing is fitted on the peripheral surface of this elliptic control lever. Therefore, to pivot the lock bushing smoothly, the inside diameter of the lock bushing must be large. As a result, a large wobble develops in the lock bushing, so that the lock bushing and positioning pin together produce a noise and the operation does not proceed smoothly.
In addition, because the lock solenoid is mounted on the control lever as a movable member, the wire must be made of a material resistant to repetitive bending and be long enough to prevent breakage. Therefore, the wire material becomes expensive and the length of the wire increases to accommodate the number of clips required for fastening the wire, thus raising the production costs. In addition, because the lock solenoid moves together with the shift lever, the lock solenoid requires enough space to move, and hence, the whole device must be large.
Further, because the action of the lock releasing lever is transmitted to the lock bushing through intermediates and the lock releasing layer cannot directly pivot the lock bushing, the number of parts increases, therefore increasing the production costs and complicating the adjustment of the parts.